This fixes a build issue with MSVC. While MSVC imports *functions*
from DLLs automatically when building a consumer of the DLL, it does
not import *variables* automatically. In these cases, we need an
explicit __declspec(dllimport).
This commit simply changes our logic to what the libtool manual
suggests, which has a very comprehensive writeup on the topic. Note
that in particular, this solution is carefully designed not to break
static linking. However, as described in the libtool manual,
statically linking the library with MSVC will output warning LNK4217.
This is still the best solution overall, because the warning is
merely a cosmetic issue.
It's subtle, since it is actually only touched by hashfp (though
we assert it's non-NULL), but give explicit advice in the default
case.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Identifiers starting with an underscore and followed immediately by a capital letter are reserved by the C++ standard.
The only header guards not fixed are those in the headers auto-generated from java.
The use of static makes this somewhat redundant currently, though if
we later have multiple compilation units it will be needed.
This also sets the dllexport needed for shared libraries on win32.
